Atmospheric Sciences
Hailstones fall from clear Spanish skies
On Jan. 8, news spread through the media in Spain that a chunk of ice fell from clear
skies and hit a car in Tocina, a village close to Seville. The piece broke into two pieces,
one weighing 1.2 kilograms and the other 1.7. Between Jan. 8 and Jan. 31, at least 50
such falls were reported.
Documented references of blocks of ice falling
from clear skies go back to the first half of the
19th century (e.g. 1829 in Córdoba, Spain: 2 kg;
1851 in New Hampshire: 1 kg). Recent cases
include a 9-kilogra, fall in Batley, West Yorkshire
in 1991. Probably the best-documented fall of an
ice chunk was April 2, 1973, in Manchester,
England. The block weighed 2 kilograms and
consisted of 51 layers of ice. Its origin was not
determined.
Though some of the recent falls in Spain have
been confirmed as practical jokes perpetrated after
initial reports of the phenomenon — people froze
large quantities of tap water and left the blocks of
ice close to a public area or road — we have
verified the authenticity of nine falls (more than 10
kilograms of ice) that occurred from Jan. 8 to Jan.
17.
This chunk of ice from Chilches (in
Chemical and isotopic analyses were performed in eastern Spain) weighed four
five of the specimens. Our results offer evidence kilograms
and measured 20 by 26 centimeters.
of chemical and isotopic heterogeneity (even
Martinez-Frias et al.
within each block), with large densities of ions —
up to five times larger than normal meteoric waters
— and corresponding to solutions of halite, calcite,
anhydrite and quartz or feldspar aerosols.
The distribution of the samples on Craig’s meteoric water line suggests either a
variation in condensation temperature or isotopic exchanges during the formation of
each ice chunk. These data, together with the high frequency of the events, indicate that
the chunks aren’t minicomets and didn’t come from aircraft. They may result from an
atmospheric phenomenon.
A hailstone is a product of the updrafts and downdrafts that develop inside the
cumulonimbus clouds of a thunderstorm, where supercooled water droplets exist. The
change of droplets to ice necessitates not only a temperature below 0 degrees Celsius,
but also a catalyst in the form of tiny particles of solid matter that become freezing
nuclei. Continued deposits of super-cooled water cause the ice crystals to grow into
hailstones. Hailstones have been found as large as grapefruits and weighing up to 7.5
pounds.
The possible explanation for how the recent ice chunks form may hinge on the classical
nucleation and growth processes. We assume that at the high region of the atmosphere
(i.e., 6 kilometers) the vapor water saturation may be near equilibrium. It is well known
that both the energy of nucleation and the critical nuclei that can eventually grow tend
to infinity if saturation is close to one. Therefore the ice could not be formed under
these conditions. However, if conditions for extra cooling exist — large concentrations
of ions, aerosols, etc — then the nucleation energy reduces (heterogeneous nucleation)
and the nuclei that can grow are formed. Another possibility could be that a crystallite
from the lowermost stratosphere enters a region of humidity, where it begins growing.
Ozone distribution maps from NASA show that, on Jan. 5, a thin jet of ozone
depression passed through all the areas in Spain where the ice falls took place. It is
commonly posited that global warming and ozone depression are linked. Despite the
fact that the greenhouse effect leads to an increase in the global mean surface
temperature, it leads to cooling in the stratosphere. Perhaps the aforementioned
nucleating crystallites enter the upper troposphere. There, where humidity is more
abundant, they start growing, evidencing that the greenhouse effect is beginning to
show. We suggest paying more attention to the fall of these unusual chunks of ice,
which could be indicating that changes are taking place in the atmosphere.
Submitted by:
Jesús Martínez-Frías, Departamento de Geología, Museo Nacional de Ciencias
Naturales, Madrid, Spain; Fernando López-Vera, Departamento de Geología,
Geoquímica y Química Agrícola, Madrid, Spain; Nicolás García, Laboratorio de
Fisica de Sistemas Pequeños, Madrid, Spain; Antonio Delgado, Departamento
de C.C. de la Tierra y Química Ambiental, Granada, Spain; Roberto García,
Laboratorio de XRD y Electroforesis, MNCN, Madrid, Spain; Pilar Montero,
Instituto del Frío, Madrid, Spain